This invention relates to a mass flow measuring device in particular but not exclusively for use in eg. harvesting machines, grain silos and hoppers.
An example of the mass flow or bulk flow of so-called xe2x80x9cbulk materialxe2x80x9d is the flow of grain to the grain tank in a combine harvester. It is known to provide a flow meter that operates by measuring forces of this flow on a sensor surface. Such flow meters may also be employed in eg. hoppers, silos, harvesting and cutting machinery other than combine harvesters, conveying machinery and various kinds of manufacturing and medical apparatuses.
Bulk flow may also embrace, eg. the flow of bulk grain and chemicals in transport vehicles (such as tankers, ships and railway tanker wagons); the flow of eg. powders, and materials of larger particle size such as fruit, vegetables, coal, minerals and ores; and even the flow of liquids of high viscosity. Thus the invention may be of use in the elevating of liquids whose viscosity changes over time. In general terms, bulk flow of material may in this context be regarded as any flow of matter in contact with a surface, in which the effects of friction between the surface and the material usually influence the maximum flow rate, and in which the matter exhibits free flow behaviour.
EP-A-0 853 234 includes a discussion of the applications of mass flow meters, for measuring the mass flowrate of bulk materials, in the combine harvester art; and also a discussion of some prior art mass flow meters. The entire description of EP-A-0 853 234 is incorporated herein by reference.
The arrangement of EP-A-0 853 234 is a highly successful apparatus for measuring the mass flowrate of eg. grains in a combine harvester, without reducing or interrupting the flow of grains. The invention seeks to provide additional advantages over those arising from mass flow meters such as, but not limited to, the EP-A-0 853 234 arrangements and methods.
In a combine harvester the grain elevator lifts grain between the grain cleaner and the bubble up auger that in turn transfers the grain to the grain tank.
The elevator includes a chain that is usually an endless ovaloid or similar shape that is wrapped at its lower and upper ends around, respectively, a drive sprocket (at the lower end of the elevator) and a tensioning (driven) sprocket (at the upper end of the elevator).
The elevator chain supports a series of elevator paddles that move with the chain during operation of the elevator. The paddles pick up grain at the base of the elevator, convey it to the top thereof and then, by virtue of the loci of the paddles (that are dictated in turn by the shape of the chain) throw the grains outwardly at the top of the elevator. The trajectories of the grains are constrained by the interior walls of a hollow, concave elevator head that encloses the otherwise open upper end of the elevator.
The elevator head guides the grains to a bubble up auger that conveys the grains to the grain tank of the combine harvester.
In the flow path of the grains between the elevator and the bubble up auger it is known to install the sensor surface of a mass flow measuring device (meter) eg. as disclosed in EP-A-0 853 233 or EP-A-0 853 234. Typically the walls of the elevator head act as a lead-in guide surface for guiding the grains into contact with the sensor surface.
GB-A-2364288 and EP-A-1169905 disclose a mass flow measuring device that is suitable for use in the arrangements described above. The measuring device of GB-A-2364288 and EP-A-1169905, the entire disclosures of which are incorporated herein by reference, includes:
a rigid anchor member that is rigidly secured to the elevator head;
a rigid mounting member having rigidly secured thereto a sensor surface assembly;
a resiliently deformable connection; and
a load cell
connected in series in a load transferring circuit.
This form of measuring device is conveniently compact. The resiliently deformable connection and the load cell confer flexibility on an otherwise substantially rigid structure. Since there are two flexible components in the load transferring circuit the overall stiffness of the device may be controlled, by selecting the stiffness of the resiliently deformable connection and the load cell respectively.
The anchor member and the mounting member are spaced from one another by the resiliently deformable connection. In practice the anchor member, the mounting member and the resiliently deformable connection are formed (eg by machining) from a solid block of a preferred metal, with the resiliently deformable connection defining an elongate web interconnecting the two members.
Two rigid, sensor fixing members are secured to and extend forwardly of the mounting member. The sensor fixing members have secured thereto a sensor member or plate as described hereinabove. The sensor fixing members additionally each perforate the web defining the resiliently deformable connection and extend rearwardly of the device. This feature allows the mounting on the device of a counterbalance weight that counteracts the mass of the sensor plate thereby rendering the net moment on the load cell zero unless a bulk flow impacts the surface of the sensor member.
The load cell is secured on the exterior of the device, overlying the anchor plate. One end of the load cell is bolted or otherwise rigidly secured to the anchor plate. The other end of the load cell is secured by means of a rigid link, in the form of a threaded rod, to the mounting plate. Since the load cell overlies the anchor plate the latter is perforated to allow the threaded rod to pass therethrough and engage the mounting plate.
The arrangement of GB-A-2364288 and EP-A-1169905 is advantageously compact; but it suffers from the following disadvantage:
The stiffness of the resiliently deformable connection is such that only a comparatively small part of the moment, caused by the bulk flow on the sensor surface, acts via the load cell.
When the measuring device is installed in a combine harvester or a similar powered device, temperature fluctuations arise in the vicinity of the measuring device. Such fluctuations result principally from the generation of hot air by the combine harvester engine.
The temperature fluctuations cause expansion and contraction of the rigid link. Because of the stiffness of the resiliently deformable connection such expansion and contraction applies a force to the load cell, by virtue of the load transferring circuit in which the components of the device are connected. In practice therefore the load cell no-load output voltage rises as the combine harvester engine temperature increases. It follows from this that the accuracy of the measuring device deteriorates as the combine harvester engine heats up.
According to a first aspect of the invention there is provided a mass flow measuring device for an elevator including an elevator head, the mass flow measuring device comprising:
a rigid anchor member that is rigidly securable to a said elevator head;
a rigid mounting member that is rigidly securable to a sensor surface assembly;
a resiliently deformable connection; and
a load cell connected in series in a load transferring circuit, the resiliently deformable connection and the load cell respectively interconnecting the anchor member and mounting member as mutually unconnected elements of the load transferring circuit, whose axes of bending are non-coinciding; and the mounting member having rigidly secured thereto one or more sensor fixing members extending externally of a boundary of the mounting member, the device being characterised in that one end of the load cell is secured to a said fixing member externally of the mounting member.
Connecting the load cell in this way, so as to lengthen the moment arm giving rise to moments acting on the load cell, greatly reduces the influence on the is load cell output of expansion and contraction of components connected to the load cell.
The feature of the resiliently deformable connection and the load cell including respective axes of deformation that are non-coinciding in use of the grain elevator ensures that the stiffnesses of the load cell and resiliently deformable connection are additive, thereby assuring operation of the measuring device.
Preferably the distance between the resiliently deformable member and the location, on the sensor fixing member, to which the load cell is secured is approximately 80 mm.
This preferred moment arm dimension has been found to reduce the relative reaction moment experienced at the load cell to about 15% of that arising in the prior art arrangement, assuming the same stiffness of the load cell and the resiliently deformable connection.
The drift of the zero (no load) voltage, and the sensitivity of the signal to mechanical stresses, are comparably reduced. Such stress is induced during eg. during the assembly of the measuring device to the elevator structure.
In the prior art arrangement of GB-A-2364288 and EP-A-1169905 the equivalent moment arm dimension is about 20 mm.
Conveniently the device of the invention includes a rigid link by which the load cell is secured to the sensor fixing member, the rigid link being secured at its ends respectively to the load cell and the mounting member; at least one so secured end of the link being threadedly received.
As in the case of the prior art device, the use of at least one threaded connection of the rigid link between the sensor fixing member and the load cell allows for pre-loading of the load cell (eg during manufacture or setting up) so as to set a desired zero (no load) voltage output.
Preferably the device includes a pair of the sensor fixing members each rigidly secured to the mounting member and extending parallel to one another; the device including a mass flow sensor member secured on the sensor fixing members externally of the mounting member. This arrangement is advantageous in:
(i) allowing mounting of the device of the invention such that most of its components, except the sensor plate, lie externally of the harsh interior environment of the grain elevator or similar conveyor with which the device is used; and
(ii) allowing the load cell to extend obliquely relative to the upper surface of the anchor member. This feature allows the achievement of the desired moment arm length whilst maintaining reasonably compact overall dimensions of the device.
The use of two, spaced fixing arms also allows stable mounting of the sensor member.
In preferred embodiments of the invention the anchor member, the mounting member and the resiliently deformable connection are integral with one another. More specifically the anchor member and the mounting member each include a rigid plate, the plates being spaced from one another by the resiliently deformable connection. The resiliently deformable connection may preferably include a web of material interconnecting the anchor and mounting members.
The foregoing features confer similar advantages, in the device of the invention, as in the device of GB-A-2364288 and EP-A-1169905.
Preferably the or each sensor fixing member perforates the web of material. This conveniently permits the mounting of one or more counterbalance weights on the sensor fixing members, on the opposite side of the rotation axis of the resiliently deformable connection to that on which the sensor member is secured. The proper choice of the counterweight allows the locating of the centre of gravity of the movable sensor members at the rotation point of the resiliently deformable connection. Consequently a zero net moment acts on the connection, unless the sensor experiences forces arising from the bulk flow of material thereon (or from a pre-load achieved through adjustment of the length of the rigid link as aforesaid). The location of the centre of gravity also eliminates the influence of the forward inclination of the vehicle on the sensor reading during uphill or downhill travel.
The invention is also considered to reside in a conveying apparatus for a bulk flowable material, the apparatus comprising a mass flow sensor including a sensor member in a flow path of bulk material, the sensor member having rigidly secured thereto one or more sensor fixing members of a device according to the invention as defined herein; and the anchor member of the device being fixed relative to a part of the conveying apparatus whereby the bulk flow of material impinging on the sensor member causes the transfer of loads via the load transferring circuit such that the load cell generates a signal indicative of the mass flowrate of the bulk material in the conveyor.
Preferably the conveying apparatus is constituted as an elevator (such as a grain, chaff or tailings elevator) in a combine harvester. Other types of conveying apparatus (eg in hoppers, silos, stores, trailers, wagons and in other kinds of harvesting machinery) are possible within the scope of the invention.